Dear Iviskel. I've wanted to ask this same question! Maybe someone can explain how the CPM changes each month? In August my CPM was 4.01 for 4,086 Impressions, while in September 436 Impressions was 3.59 CPM and I notice that each day the CPM fluctuates. I guess this is a variable rate based upon the agreement between payee and purchaser of impressions on their websites. It basically represents a ratio. The amount paid per impression is calculated by dividing the CPM by 1000. A $10 CPM equals $.01 per impression. I hope this was not more confusing than instructive.
CPM represents the cost per thousand impressions.